code: def helper_test_multivariate_duplication_equality(
      self, metric, **kwargs
  ):
      test_cases, kwargs = self.get_test_cases(**kwargs)
  
      for s1, s2 in test_cases:
          s11 = s1.stack(s1)
          s22 = s2.stack(s2)
          # default intra
          assert (
              round(
                  abs(
                      metric(s1, s2, **kwargs)
                      - metric(s11, s22, **kwargs)
                  ),
                  7,
              )
              == 0
          )
          # custom intra
          assert (
              round(
                  abs(
                      metric(
                          s1, s2, **kwargs, reduction=(lambda x: x[0])
                      )
                      - metric(
                          s11, s22, **kwargs, reduction=(lambda x: x[0])
                      )
                  ),
                  7,
              )
              == 0
          )
  
imports: import numpy
  import pandas
  import pytest
  from darts import TimeSeries
  from darts.metrics import metrics
label_desc: Use image node_id 5 for calling the TestMetrics obj's underlying member method code with example usage: obj.helper_test_multivariate_duplication_equality(metric) without return types